The invention relates to methods of and apparatus for electrophoretically varying the concentration of a colloidal solution by separating therefrom an electrically-influenceable first phase, which phase is generally present in the solution in the form of fine particles. Such techniques are exemplified, e.g., in U.S. Pat. No. 3,847,785 issued to W. B. Allington on Nov. 12, 1974; U.S. Pat. No. 3,799,863 issued to R. A. Zeinah on Mar. 26, 1974; U.S. Pat. No. 3,773,648 issued to Welzen et al on Nov. 20, 1973; and U.S. Pat. No. 3,821,102 issued to J. C. Fletcher on June 28, 1974.
In known techniques of this type, the first phase to be separated is removed from the solution by applying an electric field across a guide path through which the solution to be concentrated is passed. Up to now, this procedure has not exhibited a high selectivity of separation of the desired first phase from the colloidal particles of the solution, despite a relatively high expenditure of electrical energy for applying the field across the guide paths. In addition, even the relatively inefficient separation of the first phase has been slow.